In many shops, there was an overhead cash railway system. When your mother paid for her goods, the shop assistant put the money and a handwritten bill into one of these contraptions and sent it whizzing across the ceiling to a central cashier, who sat at a desk behind glass. She took the money, receipted the bill, which she sent together with any change whizzing back to the assistant. We children were absolutely fascinated by these systems and never got tired of watching them.